摘要:由于可降解的聚合物作为药物载体可以使得药物释放具有较高的靶向性、药物释放更加平缓,特别是可以使一些不稳定、半衰期短的药物在人体内达到可控制释放的效果,因此将可降解聚合物应用于药物释放体系中作为药物载体得到了较深入的研究。随着研究的深入,通过数学方法模拟或预测聚合物载体的降解过程以及聚合物降解过程中药物的释放行为是控释体系设计与应用的一个重要发展方向。由于影响因素较多,将所有因素逐一考虑将使得数学模型过于庞杂而失去实际意义,所以一个数学模型通常只考虑最主要几个的影响因素,并对药物释放系统进行相应的假设。目前文献中报道的降解(溶蚀)控制药物释放体系的数学模型大致可以分为两类:假设药物释放按照零级过程(zero order process)进行的经验模型和考虑影响药物释放的多种物理化学过程(如局部传质、化学反应)的理论模型。本文综述了这些理论模型及其研究进展。
摘要:Segmented polyurethane (PUR) elastomers with different soft segments (polyether,polyester,polysiloxane) and molecularly uniform hard segments,based on 1,5-naphthalene diisocyanate (NDI) and1,4-butanediol (BDO),were synthesized.They served as model elastomers for detailed investigations of the structureproperties- relations of the hard segment phase of technologically relevant NDI based elastomers.The amount of microphase separation and with that the melting points and heats of fusion rose with increasing hard segment length and decreasing strength of the hydrogen bonds between the urethane NH groups and the soft segment O atoms in the order polyester,polyether and polysiloxane.Multipeak behaviour at the melting of the hard segments indicated the formation of semi- crystalline NDI/BDO hard domain regions,which transformed into better ordered crystalline domains on annealing.At temperatures above180℃,decomposition reactions of the NDI/ BDO hard segments were initiated by breaking the hydrogen bonds.This process began in the badly ordered areas of the semi-crystalline hard segment domains.Rapid decomposition occurred at temperatures above250℃. The dynamic mechanical behaviour of the NDI based polyether elastomers showed a higher hard domain stability than elastomers based on other diisocyanates.They showed also in the service temperature range the highest storage modulus value G′over the broadest temperature range.This indicated a higher and less temperature dependent stiffness as well as a stronger effect as an active filler of the NDI/BDO hard segments.
关键词:Polyurethane elastomers;Naphthalene diisocyanate;Segmented polyurthanes;Monodisperse hard segments;Structure property relationships